If I am correct, what Trikos is saying is exactly how I had my old pro logic yamaha set up with my sub.

I had to remove the receiver's jumpers between the line out and line in signals for left and right mains. then I cabled the outs to the sub ins, sub outs back to the receiver ins, thereby using the sub's crossover.

On a 5.1 setup, however, this wouldn't help filter further from the surrounds or center channel, which carry a good amount of LF signals.

Newbie, the one thing to keep in mind is that Low Frequencies are non-directional, in other words the human ear can't pinpoint the source as with high freqs, so you won't find much advantage to using the LFM's crossover unless your receiver is doing a poor job. Trikos speaks the truth, though; using the receiver's internal crossover and letting the LFM take the <80hz signals will likely improve the performance of your receiver and your speakers.

If you want your speakers to run full range, just set the sub to run LFE only. If I recall correctly, this will only send the .1 signals in 5.1 [7.1, etc] digital signals to it. All lower frequencies intended for the other speakers will go on through without using the Onkyo's crossover.